1. Field of the Invention
The present invention relates to a sheet conveying apparatus and an image forming apparatus, and in particular, to a configuration of a skew feed correcting portion that corrects possible skew feed of a sheet.
2. Description of Related Art
Image forming apparatuses such as copiers, printers and facsimile machines conventionally include an image forming portion and a sheet conveying apparatus that uses conveying rollers to convey a sheet to the image forming portion. In the conventional image forming apparatus, a sheet may be fed obliquely when conveyed because the conveying rollers are deformed or misaligned. In the image forming apparatus, the accuracy of an image forming position with respect to the sheet depends significantly on the position of the sheet with respect to the image forming portion. Thus, accurately aligning the sheet with the image forming portion is an important factor for image quality.
In the conventional image forming apparatus, the sheet conveying apparatus includes a skew feed correcting portion to correct possible skew feed of a sheet, thus improving the accuracy of the image formation position. An example of such a skew feed correcting portion includes a shutter biased by a spring in a direction opposite to a sheet conveying direction and with which a leading end of the sheet is brought into abutting contact (see Japanese Patent Application Laid-Open No. H09-183539 and Japanese Patent Application Laid-Open No. 2010-235259 and Japanese Patent Application Laid-Open No. 2011-079608).
FIG. 13 is a perspective view showing a configuration of a conventional skew feed correcting portion. As illustrated in FIG. 13, a sheet P conveyed by a conveying unit (not illustrated in the drawings) is transferred to a nip formed by a driving roller 91 (91a and 91b) and a driven roller 92 (92a and 92b). The driven roller 92 is rotatably supported by a driven roller shaft 94. A shutter member 95 is pivotally movably mounted on the driven roller shaft 94.
The shutter member 95 includes abutting portions 95a and 95b at the opposite ends thereof in a width direction orthogonal to the sheet conveying direction. The abutting portions 95a and 95b come into abutting contact with the conveyed sheet P. The abutting portions 95a and 95b are positioned upstream, in the conveying direction, of the nip formed by the driving roller 91 and the driven roller 92. The shutter member 95 is biased by its own weight or a spring member in the direction opposite to the sheet conveying direction.
The leading end of the sheet is come into abutting contact with the abutting portions 95a and 95b of the shutter member 95. The sheet P is looped with the leading end of the sheet P coming into abutting contact with the shutter member 95 so as to follow the shutter member 95.
When the sheet P follows the shutter member 95 while being looped, the skew feed of the sheet P is corrected. When the leading end of the sheet P follows the shutter member 95, the stiffness of the looped sheet P subsequently allows the sheet P to pass through the shutter member 95 while pivotally moving the shutter member 95, against the spring, which acts to bias the shutter member 95. After the trailing end of the sheet P passes through the shutter, the shutter member 95 is returned, by the bias force of the spring, from a position where the shutter member 95 is retracted from a conveying path back to a home position. The shutter member 95 comes into abutting contact with a stopper and is held at the home position.
In the conventional sheet conveying apparatus including the skew feed correcting portion and the image forming apparatus including the sheet conveying apparatus, the shutter member 95 requires a given time to return from the position where the shutter member 95 is retracted from the conveying path to the home position. Moreover, upon returning to the home position, the shutter member 95 collides against the stopper and bounds several times due to this shock.
In particular, as illustrated in FIG. 13, if the shutter member 95 is pivotally movably mounted on the driven roller shaft 94 so as to partly cover the driven roller 92, the distance between the shutter member 95 and the driven roller shaft 94 is longer than the diameter of the driven roller 92. In this case, the shutter member 95 has an increased moment of inertia, which increases the number of bounds, requiring more time to completely return to the home position.
When a longer time is required for the shutter member to completely return to the home position, the sheet may be conveyed to the skew feed correcting portion before the shutter member completely returns to the home position. In this case, the skew feed of the sheet cannot be reliably corrected, and the capability of correcting the skew feed varies. When, for example, a long distance is set between one sheet and the succeeding sheet in order to prevent the variation in the capability of correcting the skew feed, the productivity of the image forming apparatus is hindered from being improved.
In view of the above-described circumstances, an object of the present invention is to provide a sheet conveying apparatus and an image forming apparatus which enable a reduction in the return time and bound time of the shutter.